This invention relates to an integrated circuit full wave bridge rectifier and more particularly to such a rectifier formed in a monocrystalline silicon body.
Although full wave bridge rectifier circuits employing discrete semiconductor junction diodes are well known, the incorporation of such a circuit in an integrated silicon circuit is not known. The major obstacle to so doing is the prevention of the creation of unwanted parasitic transistors when using known structures of integrated circuit diodes, particularly as it is desirable to connect one of the d.c. output terminals of the bridge circuit to a circuit ground point which point is electrically common with the bulk doped silicon body.
For example, the bulk doped body typically contains a low concentration of P-type impurities, and an epitaxial layer is grown over the surface of the body and is lightly doped with N-type impurities. Other functional circuits such as amplifiers, signal invertors, etc., are formed by known techniques in the epitaxial layer and may require a positive d.c. power supply voltage, Vcc relative to a ground point that is most conveniently connected ohmically to the P-body. Thus an integrated bridge rectifier to be integrated in a portion of the same body will have two diodes whose anodes are electrically connected to the P-body. To form these diodes, each in a pocket of the epitaxial layer, it would be standard practice to create a P-type region in the pocket and make ohmic contact to the pocket and the P-type region. The pocket is normally defined and isolated by diffusing and driving P-type impurities about the pocket in the form of an isolation wall and making ohmic ground connection to the wall and in this case the P-type anode region of the diode. However, the surrounding epitaxial material acts as a collector of a parasitic NPN transistor, the wall acting as its base and the epitaxial pocket as its emitter. During periods when the diode is forward biased, very large currents are injected into the external epitaxial regions that tend to reduce the rectifier efficiency to very small levels and in fact tend to destroy the metallized contact to the cathode.
It is therefore an object of this invention to provide an integrated full wave bridge rectifier in a silicon body that may serve as a d.c. power supply for other circuits integrated in the same body.
It is a further object of the invention to provide an integrated full wave bridge circuit having good efficiencies and having only minor parasitic currents.